You can use the Set-AzCosmosDBAccountRegion cmdlet to update the regions that an Azure Cosmos DB account uses. You can use this cmdlet to add a region or change the region failover order. The cmdlet requires a resource group name, an Azure Cosmos DB account name, and a list of regions in desired failover order1.
For your scenario, based on the PowerShell command, you are using the Set-AzCosmosDBAccountRegion cmdlet to update the regions for an Azure Cosmos DB account named account1 that is configured for automatic failover. The command specifies two regions: West US and East US. The effect of running the command is that the account will be configured for multi-region writes.
Multi-region writes is a feature of Azure Cosmos DB that allows you to write data to any region in your account and have it automatically replicated to all other regions. This feature provides high availability and low latency for write operations across multiple regions. To enable multi-region writes, you need to specify at least two regions in your account and set them as write regions2. In your command, you are setting both West US and East US as write regions by using the -IsZoneRedundant parameter with a value of $true for both regions.